Machining A Replacement Cross Slide For A Logan 11" (as Promised)

[Rex Walters]

As promised, herewith are my experiences thus far machining a replacement cross-slide casting from Andy Lofquist at Metal Lathe Accessories to fit my Logan/Wards 11" lathe.

As I described in another thread, I want to replace the rather short cross-slide that came with the lathe originally. I want to replace it with a much longer one with tee-slots in the rear (so that I can use a rear-mounted toolpost, rear-mounted boring bar holder, etc., without necessarily removing the compound slide). Unfortunately, the drawings that Andy made are for a South Bend lathe which uses a different attachment mechanism for the compound slide.

As described in the previous thread, the trickiest thing to wrap my head around before getting started was how to mill the circular tee slot. Please see that thread for details.

This is just the first of likely several posts in this thread.

Here's a shot of the original cross-slide (with the guide nut installed):




The first thing I did was to mill the bottom of the casting to use as a reference surface for all subsequent tasks. Unfortunately I didn't take any photos of this, but I just used a flycutter to flatten the "ways" on the bottom, then used an end-mill to clean up the center channel. I then used this bottom surface as a datum plane to mill the sides roughly square and the top roughly parallel.

At this point I discovered just how janky the cheap milling vice I purchased is — even with the quill of the mill trammed within a thou of the mill table, the vice itself was quite a bit out of tram (several thou). Sigh. Not a big deal at this point where I'm just rough milling. I'll deal with it later.

Next I milled the tee-slots in the rear:


After getting things in better tram, I used my nice carbide end-mill to better clean up the top (notice the vacuum sucking up swarf — cast iron is messy messy messy and even with ways covered it tended to get everywhere):



Next I cleaned up the sides a bit more (bad practice having the clamp jacks over a slot like that — should have used pieces of scrap to span the gap):



That carbide end-mill sure leaves a beautiful finish on the cast iron.

Now I was ready to start on the dovetail slot on the bottom. First I used some quarter-inch dowel pins and a micrometer to carefully measure everything on the original. Distance from the side to the bearing (non-gib) side of the dovetail, and distance between the dovetail sides. I also depth mic'ed the distance from the bottom bearing surface to the non-bearing parallel inside surface.

Once again I should have taken pictures of the measuring. I'll post some pics of the process tomorrow. The only remotely clever bit was using an adjustable parallel to measure the distance between the two dowel pins.

I used the straight carbide endmill to widen the slot roughly to size (to my great annoyance, I actually overshot a bit, but fortunately it was on the gib side). Then I got out the 60 degree dovetail cutter and went to work:



Because my workholding kind of sucked (I should have just clamped down on the top surfaces, but somehow convinced myself I didn't have room and needed clearance on top) I took very light cuts each pass.

After I had both sides cut I just had to try it out, of course, to ensure I hadn't done anything wildly wrong to this point:



It fit great, and more importantly, it passed my very basic tests:

1. I put a mag base dial indicator on top, and measured the deflection on a faceplate as I slide the top-slide for and aft (while pushing the whole top-slide to the right by hand to ensure it was bearing on the dovetail surface). Total deflection was just two or three tenths over about 5.5 inches.
2. I took the short gib from the original and ensured that there was room to slide it in on the right side with very little room to play. (I haven't machined the new long gib yet, so it won't fit vertically.)

That's as far as I've gotten so far. I will finally be able to get into the shop tomorrow to start on the remaining work:

1. Machining the angles on the short sides of the gib.
2. Boring and tapping the holes in the right side for the gib screws.
3. Boring and pressing a locating pin on the right side of the casting as well as a corresponding hole in the gib (to prevent it shifting fore and aft)
4. Machining the circular tee-slot to attach the compound.
5. Boring a press-fit hole for the center locating pin for the compound (and pressing in the 0.5" pin)
6. Boring and tapping the workholding holes on the top of the slide
7. Machining appropriate bits to attach the nut for the crossfeed screw.
8. Final lapping and scraping of all bearing surfaces (something I've never attempted)
9. Doubtless dozens of other things I'm forgetting (like painting — God I hate painting)

Whee!

 

[Ulma Doctor]

nice work, i'm looking forward to the progression.

 

[clivel]

It looks great so far Rex, I am following along with interest as I would eventually like to do the same for my Logan 200.
One question though, the swivel area on the original Logan cross-slide is raised above it's surface, is the new casting thick enough to ensure that the top-slide won't be sitting too low?

As I was typing this it occurred to me that rather than trying to cut the circular t-slot, it may just be simpler to look out for a South Bend top-slide instead.
Clive

 

[Rex Walters]

... is the new casting thick enough to ensure that the top-slide won't be sitting too low?

Definitely. Actually, even after milling a considerable amount off the top and bottom I've left it a little thicker than the original (I'll have to readjust all my QCTP holders regardless). Original is about .900" from top raised lip to bottom surface. When I'm done I expect the new casting to be just over an inch.

I'm also enjoying the challenge of milling it for the stock Logan compound. I've not seen that documented anywhere, so I thought I'd give it a shot.
--
Rex

 

[eeler1]

The gib on mine has indents where the tightening screws are located, instead of a pin to prevent it slipping. Might be one less hole to drill in that cast iron. Just a thought.

Nice write up and pics. I'll be watching to see how it works out.

 

[Rex Walters]

The gib on mine has indents where the tightening screws are located, instead of a pin ....

George Thomas felt the pin important enough that he devoted a few pages of his book (The Model Engineers Workshop Manual) to the topic!

"The usual arrangement is for the gib-strip to be held into contact with one side of the dovetail slide by means of pointed screws which touch the bottoms of dimples as shown at (1). These would be quite effective if the slide never had to move, but movement is what the slide is for! When the slide is wound along in either direction, the frictional drag against the gib-strip will produce a wedging action at the tips of the screws which will, in turn, tighten the slide. There have been many complaints on this score from readers in the past and the remedy is a simple one — fit a dowel into the gib-strip and so prevent any end movement in relation to the screws."
​

Makes sense to me, so I'll add a pin as he suggests (and I note that my old cross slide did have a pin, despite the fact that the machining "does not readily lend itself to quantity production methods").

That chapter also reminds me that I want to add gib locks as well (added to the list). I'll probably add two locking screws, fore and aft.

(That also reminds me that I want to make a handwheel to manually turn my feed-screw on my lathe. That will allow me to do precise movements in Z along the bed by simply engaging the half nut.)

I milled the bevels on the gib this morning. I'll post photos after lunch.
--
Rex

 

[Rex Walters]

Here's how I used 0.250" dowels to measure the original cross-slide:

First I measured used a depth mic to measure the distance from the bottom surface to the inner surface. Then I measured the distance from the side to the edge of the dowel. I just milled the bevel in the new slide at the same depth, and kept moving the cutter horizontally each pass until the side t0 dowel-side distance on the new part measured the same as the original.


Then I used an adjustable parallel to span the gap between the two sides. Then I mic'ed the width of the parallel. Again, I milled the new part until this distance was the same.

 

[Rex Walters]

After milling the dovetail in the bottom of the new casting, I took some time to lap the bottom using coarse sandpaper on my surface plate (with water as a lubricant).

Next up was to mill the bevels on the gib. I had to decide whether to build a one-time-use fixture to hold the gib, or just use available tooling and figure out some way to hold the gib at the required angle to the tool. I opted for the latter.

The simplest thing I could think of was to again use dowels and my adjustable parallels (handy little suckers):


This isn't the most secure workholding in the world, but I figured it would suffice. At first I only hand tightened the parallels by squeezing the wedges with my fingers, but eventually I wised up and started tapping them tight with a small tack hammer. Also, I eventually learned that (unlike the picture shown) I should ensure that I locate the outermost dowels as close to the front and back edges of the slide as possible (to provide better support at the ends of the gib).

Then I took extremely light passes (0.005" at a time) with pretty slow feed rates (power feed). I was careful to mill in the correct direction (table moving from left to right, with the cutter moving from top to bottom as photographed above) so that the gib was pushed back into the dovetail as the leading edge of the cutter hits the gib.

It was probably unnecessary to mention this, because only a complete idiot would risk throwing a part just to save a little time by milling in both directions and taking too heavy a cut.



Ahem.

For what its worth, I'm very fortunate that I didn't chip my expensive carbide end-mill or (much worse) injure someone (me!) when the part was thrown. Even though I only had the slide lightly clamped, I was still surprised that there was enough force to pull it out of the clamps.

Lesson learned. This was when I got out the hammer to better tighten the wedges and started taking my time with light, light passes. I even slowed the feed a bit more once I started taking wider cuts as the quill was lowered.

Here's what it looked like as I was taking 0.005" at a slow feed rate (just to show how little I was actually taking off each pass).

On the first edge, I didn't mill down to a sharp knife edge. I left a tiny little bevel on the edge to ensure that I had enough material to mill the other side. I figured I'd be knocking the sharp edges off with a file when I was done anyway.


For the other edge I just flipped the part and stole the idea from Paula on the South Bend forum to use some 3/32" rod as a spacer to lift the part enough to mill. Then rinse and repeat.


Like spelling "banana," the only tricky thing about the second edge was knowing when to stop.

I wanted to ensure that the gib was narrow enough not to bind top-to-bottom in the slot, but I didn't want to mill off any more than necessary. This didn't need to be a super accurate measurement, I just didn't want the gib to bind. The solution was pretty simple, just use another piece of the 3/32" rod as a gauge on top:


The camera angle is pretty awkward, but in person it was obvious that the gib was higher than the gauge rod (the square wasn't vertical):

I just kept milling until the square tipped the other way. Here's a shot from the other side once I was just about done (I think I took off another 0.005" just for good measure). You can clearly see that the squares are touching at top, but there's a gap at the bottom.


Finally, here's a shot showing the finished gib in place on the slide (finished except for cutting it to length — I did that off camera):


In this final shot of the gib in place, you can see one little detail I forgot to mention. When I cleaned up the casting scale in the slot on the bottom of the raw casting, I was left with a trench quite a bit deeper than the original part. At first I just started milling away on the roughly-formed ways to lower the gap, but eventually I chickened out. Instead of reducing the depth to final dimension, I reasoned it was okay to leave a little more "meat" on the sides. The trench isn't a precision bearing surface anyway, it just needs to provide clearance. Here you can clearly see the little "extra" gap I'm talking about (I don't think it will hurt anything):


Next up is to bore and tap the holes for the gib screw, gib pin, and lock screws. I also need to make the lock screws.

Enjoy!
--
Rex

 

[eeler1]

I had no idea, was wondering why you were doing it that way! I'll defer to George.

 

[wa5cab]

Rex,

The height of the underside of the cross slide is important (I won't say critical). The cross feed nut attaches under there and the threaded hole in it must line up with the height of the cross feed screw. You can always shim down. But you can't shim up (you can't buy negative thickness shim stock).

Also, when deciding where to put the hole to mount the cross feed nut, be sure that there is adequate clearance for the nut to run off of the screw threads before it runs into the top of the dovetail area. The gap between the dovetails sure seems to start a long way back. And also be sure that the nut runs off of the end of the feed screw before the cross slide runs off of the dovetails or into something.